My wife reads everything by David Weber. If you can get him into those books, you’ll have Christmas presents for the rest of his life.
I recommend giving him all six of Neil Clarke’s anthologies of best science fiction short stories of the past year:
http://neil-clarke.com/the-best-science-fiction-of-the-year/
If you only buy one of these, I recommend Volume 3, which includes Suzanne Palmer’s excellent “The Secret Life of Bots”.
Elizabeth Bear has a “White Space” series. I thought that Ancestral Night was pretty meh, but I’m currently reading Machine and am liking it better. It is hard SF taking place in a “woke” future, but doesn’t pound you on the head with it with all the subtilty of a 10-pound sledgehammer like a Becky Chambers book.
And as mentioned in the original run of this thread Andy Weir has a new book out called “Project Hail Mary”. I enjoyed Artemis, but PHM was EXCELLENT! I highly recommend it!
MtM
I made this original post only a little into the book, before too many settings elements came up. It is about doctors who work in a giant, spindle-shaped space hospital that caters to (and employs) species of a very wide range of biological types and environmental needs. Doctors have the ability to upload recordings of minds, which give them additional knowledge and skills, but these recordings can be disorienting. One of the main characters is a large but fragile colorful and very friendly flying insect. The book covers solving a medical (and technological) mystery.
Yes, Machine is a new Sector General book. She does acknowledge it in the end notes, though.
it’s a quick read but is still relevant metrophage by kadrey …
As the OP mentions “Clark” – which I presume refers to Arthur C. Clarke – one thing I should mention is that there’s a complete collection of all his short stories available. As I’m a big fan of Clarke myself and particularly enjoy his short stories, and he was a prolific writer of them, I’ve found this collection to be quite the treasure. It’s available both in ebook editions and as a trade paperback (i.e.- a large-format paperback).
The Dreaming Void trilogy by Peter F Hamilton. Epic.
For an Arthur C Clarke fan let me recommend the the Chinese writer Liu Cixin, and most specifically the trilogy Remembrance of Earth’s Past.
Huge scope and ideas, and won practically every SF award there is.
Pretty much every series by him. (except the Night Alchemist, won’t spoil but I did not enjoy it.)
I love how he has a small set of initial concepts, wormholes, post scarcity, body rejuvenation/replacement and builds wildly different universes in his different book series.
I won’t gush about the Dark Forest either. The Remembrance of Earth’s Past was also very enjoyable!
I haven’t read all of his work but I agree with your general sentiment. All the fake sci-fi is utterly believable and I do so love the sweeping nature of his worlds.
And that series by Liu Cixin is indeed awesome too.
I don’t need hard science fiction, I need hard-looking science fiction 
It doesn’t meet the criteria for the OP but another series that I adore is the Murderbot Diaries. The sci-fi is more wallpaper than integral.
The wife and I love the series so much so that we named one of the new kittens, Rin.
There is also Hamilton’s most recent trilogy, the Salvation Sequence, if it hasn’t been mentioned.
Just recently read a children’s science fiction novel which was very hard SF–something that’s not so common for readers of that age. Fuzzy Mud, by Louis Sachar.